Use simpler code to draw lines

The previous code could create glitches with some PDF renderers. This new code
is simpler and corresponds to what we really want to do.

weasyprint/draw.py

@@ -741,6 +741,55 @@ def draw_rect_border(stream, box, widths, style, color):
     stream.fill(even_odd=True)
 
 
+def draw_line(stream, x1, y1, x2, y2, thickness, style, color, offset=0):
+    assert x1 == x2 or y1 == y2  # Only works for vertical or horizontal lines
+
+    with stacked(stream):
+        stream.set_color_rgb(*color[:3], stroke=True)
+        stream.set_alpha(color[3], stroke=True)
+
+        if style == 'dashed':
+            stream.set_dash([5 * thickness], offset)
+        elif style == 'dotted':
+            stream.set_dash([thickness], offset)
+
+        if style == 'double':
+            stream.set_line_width(thickness / 3)
+            if x1 == x2:
+                stream.move_to(x1 - thickness / 3, y1)
+                stream.line_to(x2 - thickness / 3, y2)
+                stream.move_to(x1 + thickness / 3, y1)
+                stream.line_to(x2 + thickness / 3, y2)
+            elif y1 == y2:
+                stream.move_to(x1, y1 - thickness / 3)
+                stream.line_to(x2, y2 - thickness / 3)
+                stream.move_to(x1, y1 + thickness / 3)
+                stream.line_to(x2, y2 + thickness / 3)
+        elif style == 'wavy':
+            assert y1 == y2  # Only allowed for text decoration
+            up = 1
+            radius = 0.75 * thickness
+
+            stream.rectangle(x1, y1 - 2 * radius, x2 - x1, 4 * radius)
+            stream.clip()
+            stream.end()
+
+            x = x1 - offset
+            stream.move_to(x, y1)
+            while x < x2:
+                stream.curve_to(
+                    x + radius / 2, y1 + up * radius,
+                    x + 3 * radius / 2, y1 + up * radius,
+                    x + 2 * radius, y1)
+                x += 2 * radius
+                up *= -1
+        else:
+            stream.set_line_width(thickness)
+            stream.move_to(x1, y1)
+            stream.line_to(x2, y2)
+        stream.stroke()
+
+
 def draw_outlines(stream, box):
     width = box.style['outline_width']
     color = get_color(box.style, 'outline_color')
@@ -873,7 +922,7 @@ def add_vertical(x, y):
                 (y + 1, x - 1), (y + 1, x)], vertical=False)
         segments.append((
             score, style, width, color, 'left',
-            (pos_x - width / 2, pos_y1, 0, pos_y2 - pos_y1)))
+            (pos_x, pos_y1, 0, pos_y2 - pos_y1)))
 
     def add_horizontal(x, y):
         if y == 0 and table.skip_cell_border_top:
@@ -896,7 +945,7 @@ def add_horizontal(x, y):
             pos_x2 = column_positions[x] + shift_before
         segments.append((
             score, style, width, color, 'top',
-            (pos_x1, pos_y - width / 2, pos_x2 - pos_x1, 0)))
+            (pos_x1, pos_y, pos_x2 - pos_x1, 0)))
 
     for x in range(grid_width):
         add_horizontal(x, 0)
@@ -914,14 +963,10 @@ def add_horizontal(x, y):
 
     for segment in segments:
         _, style, width, color, side, border_box = segment
-        if side == 'top':
-            widths = (width, 0, 0, 0)
-        else:
-            widths = (0, 0, 0, width)
         with stacked(stream):
-            clip_border_segment(stream, style, width, side, border_box, widths)
-            draw_rect_border(
-                stream, border_box, widths, style,
+            bx, by, bw, bh = border_box
+            draw_line(
+                stream, bx, by, bx + bw, by + bh, width, style,
                 styled_color(style, color, side))
 
 
@@ -1230,59 +1275,10 @@ def draw_first_line(stream, textbox, text_overflow, block_ellipsis, x, y,
     return emojis
 
 
-def draw_wave(stream, x, y, width, offset_x, radius):
-    up = 1
-    max_x = x + width
-
-    stream.rectangle(x, y - 2 * radius, width, 4 * radius)
-    stream.clip()
-    stream.end()
-
-    x -= offset_x
-    stream.move_to(x, y)
-
-    while x < max_x:
-        stream.curve_to(
-            x + radius / 2, y + up * radius,
-            x + 3 * radius / 2, y + up * radius,
-            x + 2 * radius, y)
-        x += 2 * radius
-        up *= -1
-
-
 def draw_text_decoration(stream, textbox, offset_x, offset_y, thickness,
                          color):
     """Draw text-decoration of ``textbox`` to a ``document.Stream``."""
-    style = textbox.style['text_decoration_style']
-    with stacked(stream):
-        stream.set_color_rgb(*color[:3], stroke=True)
-        stream.set_alpha(color[3], stroke=True)
-
-        if style == 'dashed':
-            stream.set_dash([5 * thickness], offset_x)
-        elif style == 'dotted':
-            stream.set_dash([thickness], offset_x)
-
-        if style == 'wavy':
-            thickness *= 0.75
-            draw_wave(
-                stream,
-                textbox.position_x, textbox.position_y + offset_y,
-                textbox.width, offset_x, thickness)
-        else:
-            stream.move_to(textbox.position_x, textbox.position_y + offset_y)
-            stream.line_to(
-                textbox.position_x + textbox.width,
-                textbox.position_y + offset_y)
-
-        stream.set_line_width(thickness)
-
-        if style == 'double':
-            delta = 2 * thickness
-            stream.move_to(
-                textbox.position_x, textbox.position_y + offset_y + delta)
-            stream.line_to(
-                textbox.position_x + textbox.width,
-                textbox.position_y + offset_y + delta)
-
-        stream.stroke()
+    draw_line(
+        stream, textbox.position_x, textbox.position_y + offset_y,
+        textbox.position_x + textbox.width, textbox.position_y + offset_y,
+        thickness, textbox.style['text_decoration_style'], color, offset_x)